Some electric discharge machining apparatuses are configured to estimate the machining time. These electric discharge machining apparatus include an electrode, a main shaft, a machining time estimation device that estimates the machining time, a power supply, and a numerical controller which drives and controls the electric discharge machining apparatus.
The machining time estimation device includes, for example, an input section that receives user's required specifications, a machining amount calculation section that calculates an amount of the workpiece that is to be removed by machining (hereinafter, “removal amount”), a machining time calculation section that calculates the machining time based on the input required specifications, a machining time data section that stores machining rate data necessary to calculate the machining time, and an output section that outputs the machining time calculated.
The estimation of the machining time is performed as follows. A user inputs the required specifications. The required specifications are, for example, electrode size, workpiece size, machining depth, and machining conditions depending upon how the workpiece is to be machined. The electrode size and the workpiece size are expressed by, for example, “x size: −5 to 5, y size: −10 to 10”. If the entire electrode is going to be inserted in the workpiece, the workpiece size does not directly affect the machining time; therefore, the workpiece size is often omitted from the specifications.
The machining amount calculation section receives the required specifications from the input section and calculates the removal amount from the electrode size and the workpiece size.
The machining time calculation section generates machining time sequences from starting conditions to finishing conditions estimated relative to the required specifications based on pieces of calculation data thus obtained and machining rate data on a machining rate per machining amount that is stored in the machining time data section in advance, and outputs the machining time sequences to a display device such as a CRT.
Japanese Patent Application Laid-Open No. 6-297250 discloses an electric discharge machining apparatus which estimates the machining time by correcting the machining rate according to the machining depth.
Japanese Patent Application Laid-Open No. 2-100822 discloses an electric discharge machining apparatus in which a shape of the electrode is input and the machining time is corrected from the shape.
However, most electrodes are of three-dimensional, complex shape. Therefore, as the machining progresses, a machining area varies with the shape of the electrode. Therefore, the machining conditions vary such as changes in a discharge state according to machining dusts deposited between the electrode and the workpiece as the machining progresses and in the machining area. As a result, the difference between the estimated machining time and the actual machining time disadvantageously grows and the accurate estimation of the machining time cannot be disadvantageously ensured only by changing the machining rate according to the machining depth as explained in the conventional documents.
Meanwhile, in the method of inputting the shape of the electrode, the shape can be input if the shape is simple such as a prism; however, the shape cannot be input if the electrode has a complex shape. As a result, the machining time cannot be estimated for complex-shaped electrodes.
Even if the electrode is simple in shape, the shape of the electrode is influenced by the subjectivity of the user who inputs the data and machining uniformity cannot be maintained. If the shape of the electrode is deviated from the characteristics of the shape input in advance even slightly, the deviation is not reflected in the machining time.
Moreover, the workpiece is often pre-machined by cutting or the like. In addition, one workpiece is often continuously machined using a plurality of electrodes having different shapes to thereby obtain the final shape of the workpiece. If the workpiece is, for example, a cellular phone workpiece, the workpiece is subjected to premachining by cutting and then to discharge machining using as many as about 20 types of electrodes having different shapes, thereby obtaining the final shape of the workpiece. As a result, the machining amount cannot be grasped only by recognizing the simple electrode shape, and the accurate machining time cannot be disadvantageously estimated.